1. Field of the Invention
The present invention relates generally to the field of circuit board inspection and repair, and more particularly, to a method and an apparatus for locating defects on a printed circuit board or the like and for facilitating the repair of located defects.
2. Description of Prior Devices
As is well known to persons skilled in the art, a printed circuit board is used for mounting and electrically interconnecting electrical components in a predetermined manner. To the extent possible, such printed circuit boards are constructed mechanically, using automated assembly machines which operate to reduce the often prohibitive costs of manually assembling a printed circuit board. While reducing overall costs, such automated assembly techniques have been found to give rise to a certain limited number of assembly defects such as incorrect insertions of components, and their leads or pins, as well as defects in the soldering procedures which then follow.
Originally, steps were taken to locate assembly errors of this general type through a visual inspection of each printed circuit board at a desired stage of the manufacturing process, by human operators using the naked eye, or possibly a stereo microscope or the like. However, since this procedure was found to be extremely tedious and inaccurate, as well as a relatively expensive process, steps were taken to develop automated systems for inspecting printed circuit boards to replace such visual inspections.
Examples of devices of this general type are the Model 5511, Model 5512, Model 5515, Model 5516 and Model 5517 Printed Circuit Board Inspection Systems which are manufactured by Control Automation Incorporated of Princeton, N.J. These inspection devices generally employ a series of cameras which are mounted within a fixture (an inspection head) adapted for controlled movement relative to a printed circuit board. The inspection head is either sequentially advanced to successive viewing field (typically one inch by one inch) established along the surface of the printed circuit board then under inspection, or continuously advanced along the surface of the printed circuit board, to acquire images for microprocessor analysis to identify potential defects. Further detail regarding the printed circuit board inspection systems which are used to perform these operations are disclosed, for example, in U.S. patent application Ser. No. 07/159,774, filed Feb. 24, 1988 and entitled "Apparatus for Inspecting Printed Circuit Boards with Surface Mounted Components", as well as issued U.S. Pat. Nos. 4,978,220 and 5,060,065, the subject matter of which is incorporated by reference as if fully set forth herein.
Following inspection of the printed circuit boards, steps must be taken to report any detected defects for appropriate correction. Early techniques involved the listing of detected defects, in memory, for subsequent display to the operator. While quite adequate in effectively identifying defects, and in reporting detected defects to the operator, such techniques were found to be somewhat limiting when later applied to the procedures involved in repairing the detected defects identified on an assembled printed circuit board.
Perhaps most significant is that in locating detected defects, and in reporting detected defects to an operator, it remained necessary for separate steps to be taken to actually locate the detected defects on the printed circuit board to be repaired at the repair station provided for such purposes. This is because the operator, upon being advised of the location of a particular defect, still had to then take steps to physically locate the defect on the printed circuit board, for repair in otherwise conventional fashion. Such techniques were found to be somewhat tedious, and at times prone to error. Further complications arose as printed circuit boards came to be manufactured with a greater number of components per unit area (i.e., more "populated"), making such visual operations even more difficult and tedious to accomplish. Recognizing the limitations of such visual operations, steps were taken to automate the procedures necessary to identify defects on a printed circuit board, for correction at a suitable repair station.
One approach to the automated location of detected defects, for repair purposes, was to provide the printed circuit board inspection system with an apparatus for marking the defects found on an inspected printed circuit board, in conjunction with the circuit board inspection procedure. To this end, ink markings were applied to the inspected printed circuit board to later draw the operator's attention to any detected defects during the repair procedure. This, in conjunction with the more traditional listing of defects identified by the printed circuit board inspection system, served to identify necessary repairs for correction.
As a means for accomplishing this, the inspection head of the printed circuit board inspection system was fitted with a separate fixture for receiving an ink marker for applying distinctive markings (dots) to the circuit boards adjacent to the detected defects. Movement of the marker along the printed circuit board was accomplished by moving the inspection head of the printed circuit board inspection system to the location of a detected defect, followed by activation of the marker so as to apply the desired marking to the printed circuit board. Since the marker was directly associated with the inspection head of the printed circuit board inspection system, such marking could be accomplished both directly and automatically making use of control functions already part of the printed circuit board inspection system (for operating the inspection head).
However, in practice, even this technique was found to exhibit certain disadvantages. One such disadvantage is that it was still necessary to in some way compare a listing of the detected defects with the markings on the printed circuit board to make sure that all marked defects had been located by the operator and corrected at the repair station. Once again, this necessitated visual comparisons by the operator at the repair station. Furthermore, it has recently become a practice in conjunction with the manufacture of certain printed circuit boards to eliminate the so-called "post-washing" procedures which had traditionally been employed following manufacture, inspection and repair of the printed circuit boards. This resulted in printed circuit boards which, although repaired, nevertheless still possessed the markings which were applied to them by the marker. Such markings are considered to be undesirable by some manufacturers of printed circuit boards, so much so that the resulting boards are often described as being "contaminated" by the markings which remain on them. The additional steps needed to remove such ink markings represent an additional manufacturing step, which is clearly undesirable.
Responsive to continued demand, steps were then taken to provide the repair station used to correct detected defects with a device which could locate detected defects for repair without requiring itemized listings or ink markings to do so. This led to the development of the Auto-Locate.TM. Repair Station which is manufactured by Control Automation Incorporated of Princeton, N.J. To this end, a substantially conventional repair station is provided with a directed light system for indicating detected defects on the printed circuit board by, in essence, pointing to them. The beam of light can be directed either responsive to signals received from the printed circuit board inspection system employed to inspect the printed circuit board, or by transferring data received from the printed circuit board inspection system to an appropriate host computer. In either case, the Auto-Locate.TM. Repair Station could, for the first time, direct the operator to detected defects on the printed circuit board without requiring the operator to consult separate listings which would then require the operator to divert attention from the printed circuit board to be repaired, and without requiring the marking of printed circuit boards with inks which would later require removal to provide an acceptable finished product.
While the Auto-Locate.TM. Repair Station was found to constitute a significant advance over prior repair systems, the ever-advancing development of printed circuit boards was found to place yet another constraint on their repair. Specifically, as the "population" of printed circuit boards increased dramatically, the spacings between adjacent features on the printed circuit boards decreased dramatically. This significantly increased the difficulty of locating defects and of making appropriate repairs without the use of enhancements such as a stereo microscope or the like. Resulting from this, it was not uncommon for the operator to have to switch between a first mode in which the operator would locate the detected defect responsive to direction of the beam of light, without using the stereo microscope, and a second mode in which the detected defect would be repaired making use of the stereo microscope. Again, this tended to require the operator to divert attention from the detected defect identified by the beam of light, leading to the disadvantages inherent in other repair procedures.
It therefore became desirable to develop a repair station including a device for identifying detected defects, and for facilitating (e.g., magnifying) their repair, in a more integrated operation which would allow both procedures (location and repair) to be performed substantially simultaneously by the operator.